Chudzik
angle explosion bonding



A ril 21, 1970 a. CHUDZIK ANGLE EXPLOSION BONDING 2 Sheets-Sheet 1Original Filed March 11, 1963 FIG.1

FIG-3 INVENTOR BRUNO CHUDZIK BY A -QT AT'TOR Y United States Patent26,858 ANGLE EXPLOSION BONDING Bruno Chudzik, Wenonah, N.J., assignor toE. I. du Pont de Nemours and Company, Wilmington, Del., a corporation ofDelaware Original No. 3,264,731, dated Aug. 9, 1966, Ser. No. 264,373,Mar. 11, 1963, which is a continuation-in-part of application Ser. No.118,376, June 20, 1961. Application for reissue Mar. 26, 1968, Ser. No.719,787

Int. Cl. B23k 21/00 US. Cl. 29-470.1 17 Claims Matter enclosed in heavybrackets appears in the original patent but forms no part of thisreissue specification; matter printed in italics indicates the additionsmade by reissue.

ABSTRACT OF THE DISCLOSURE Metal surfaces are metallurgically bondedtogether by arranging such surfaces at an angle to each other andexplosively causing them to collide progressively under bondingconditions.

This application is a continuation-in-part of copending applicationSerial No. 118,376 filed June 20, 1961 in the name of Bruno Chudzik, nowabandoned.

This invention relates to a method of bonding metals. More particularly,this invention relates to a method of bonding metals by explosive means.

In accordance with the present invention there is provided a method forforming a substantially continuous metallurgical bond between metallayers which comprises forming a juncture between at least two metallayers, said juncture being defined by an angle of at least about 1,positioning a layer of a detonating explo sive on the external surfaceof at least one of the metal layers, and initiating the explosive sothat at least one of the ratios of the collision velocities to therespective sonic velocities of the metal layers is less than 1.2 andwhen each of these ratios is greater than 1.0 the angle between each twoadjacent metal layers in the collision region exceeds the maximum valueof the sum of the deflections produced in the metal layers by obliqueshockwaves.

The term metal layer as used herein refers to a layer of a single metalor of an alloy of two or more individual metals or to a plurality ofsingle layers bonded together.

The term juncture as used herein refers to the arrangement of one metallayer with respect to the other metal layer such that the two layersmeet or substantially meet at a single point or along a single line. Ineither case, the planes in which the internal surfaces (i.e., thesurfaces to be bonded) of the two metal layers lie, intersect along agiven line, i.e., the two layers are not parallel. Hereinafter, theplanes in which the internal surfaces of the metal layers lie aredesignated simply as the planes of the two metal layers."

The expression said juncture being defined by an angle of at least about1 as used herein means that an angle, 5, between the two metal layersmeasured in any plane perpendicular to the line of intersection of theplanes of the two metal layers is at least about 1'.

The term external surface of a metal layer as used herein refers to thatsurface of the metal layer parallel to the inner surface to be bonded ofthe metal layer.

Reference is now made to the attached drawings for a. more completeunderstanding of the invention. In the drawings like numbers indicatesimilar elements and FIGURE 1 is a cross-sectional view of an assemblywhich may be used to practice the invention in which a layer of adetonating explosive is positioned on the external surface of one of themetal layers;

FIGURE 2 is a cross-sectional view of another assembly which may be usedto practice the invention in which a layer of a detonating explosive ispositioned on the external surface of each of the metal layers;

FIGURE 3 is a cross-sectional view of a bonding assembly during thecourse of detonation of explosive layers positioned on the externalsurfaces of each of the metal layers;

FIGURES 4A to 4B are top views of bonding assemblies in each of which anexplosive layer is to be initiated at a single point or along a singleline on the explosive layer;

FIGURE 5 is a cross-sectional diagram illustrating the geometry anddynamics of a bonding assembly having an explosive layer on one metalplate; and

FIGURE 6 is a crosssectional diagram illustrating the geometry anddynamics of a bonding assembly having an explosive layer on both metalplanes.

In FIGURE 1, metal layer 1 forms a juncture with metal layer 2 whichrests on a supporting means 3, e.g., of metal, wood, or gypsum cement,the angle between metal layers 1 and 2 being maintained by means of aspacer bar 4. A layer of a detonating explosive 5 to which is attachedan initiator 6 having lead wires 7 to a source of electric current ispositioned on the external surface of metal layer 1.

In FIGURE 2, metal layers 1 and 2 rest on supporting means 3. A layer ofa detonating explosive 5 to which is attached an explosive cord 8 ispositioned on the external surface of each of the metal layers and theexplosive cords 8 are attached to an initiator 6 having lead Wires 7 toa source of electric current.

Although it is not intended that the invention be limited by any theoryof operation a discussion of the mechanism by which bonding is achievedelucidates the extent to which process conditions can be varied ormodified within the sense and scope of the invention and facilitatesselection of optimum conditions for bonding in a given system.

It is believed that the formation of a continuous metallurgical bondbetween the adjacent surfaces of two metal layers or plates is dependentupon a jetting" phenomenon which occurs as illustrated schematically inFIGURE 3. When the layer(s) of explosive 5 is initiated (9 representingthe gaseous detonation products) the pressure produced by the detonationpropels the metal plate(s) upon which the explosive rests toward theadjacent metal plate. When the metal plates collide at an appropriateangle and the collision region progresses across the metal plates at anappropriate velocity the pressure produced by the collision istransmitted slightly ahead of the collision region and forces thesurface layers of the opposing metal plates to be thrown forward at highvelocity from the collision region, i.e., to form a jet 10. The removalof the surface oxides and other contaminants by the jet allows theunderlying clean metal of the two opposing plates to be brought intointimate contact thus forming a continuous metallurgical bond 11 at thecommon interface between the two plates. In some instances, the jetescapes completely from between the two plates removing the surfaceoxides and other surface contaminants from the bonded system. In otherinstances, the jetted material is trapped between the two plates. In thelatter cases the high kinetic energy of the jet causes melting of theadjacent clean surfaces of the metal plates and the melted materialrapidly solidifies providing a bonding zone characterized by thepresence of a homogeneous mixture of the metals of the two opposingplates which bonding zone contains the surface contaminants in adispersed state so that they do not hinder bonding= The bonding zone cancomprise a uniform layer of the homogeneous mixture of the metals of thetwo opposing plates or, if the trapped jet oscillates as it moves aheadof the collision region, the bonding zone may contain only discretepockets of the mixture at more or less periodic intervals across theinterface between the plates. In any event, a sound, substantiallycontinuous metallurgical bond is produced.

Since the appropriate collision angle and velocity required for jettingvary from system to system it is necessary to explain, first, how thisangle and velocity can be determined for a given system, and. second,how the process conditions can be adjusted to insure collision of agiven pair of metal plates at the required angle and velocity.

In the following discussion 1 and 2 refer to the two colliding metalplates. V and V denote the velocities of the collision region relativeto plates 1 and 2 respectively, or the velocities with which the twoplates move into the collision region; C and C represent the bulk soundvelocities of plates 1 and 2, respectively, bulk sound velocity beingdefined as the velocity of a plastic shock wave which forms when anapplied stress just exceeds the elastic limit for unidimensionalcompression of the particular metal or metallic system involved; V isthe relative plate velocity or the velocity with which the platesapproach one another and a is the angle between plates 1 and 2 in thecollision region. It is assumed that the values of V v and 1,! whichdescribe the collision are changing slowly enough as the collosionproceeds that the flow of metal in the collision region at any instantmay be described approximately as a locally steady flow.

When either V is less than C, and/or C is less than C bonding isachieved as long as V exceeds a minimum value required to producesufficient pressure in the col ision region to overcome the elasticstrength or exceed the elastic limit of at least one of the metal platesand thus provide the plastic deformation required for jetting. Theminimum relative plate velocity for any particular metal system dependson the properties of the metal plates and increases with increasingstrength, hardness, and surface roughness. This minimum value of Vnecessary for bonding stainless steel to carbon steel, for example, isabout 90 meters per second if the surfaces of the metal plates arefairly smooth.

When both V exceeds C and V exceeds C collision results in the formationof oblique shock waves in both plates. If these shock waves are attachedto the collision line, the pressure produced by the collision cannot betransmitted ahead of the shock waves, i.e., cannot be transmitted aheadof the collision region, and, therefore, a jet cannot be formed.Instead, the oblique attached shock waves sharply deflect the metalplates, leaving the surface contaminants at the interface and thuspreventing bonding. The shock waves are reflected from the external freesurfaces of the colliding plates as rarefaction waves which either causethe plates to separate at high velocity or produce spalling in one ofthe plates. If, however, V exceeds a minimum value required to make thecollision angle 11/ exceed a critical value, I the oblique shock wavesbecome detached from the collision region and stand ahead of thecollision line. In this situation pressure is transmitted ahead of thecollision region causing jet formation and making bonding possible. Thevalue of this critical angle differs from system to system and isdependent upon V and Vcg, and upon the material properties of metalplates 1 and 2.

When both V exceeds 1.2 C, and V exceeds 1.2 C good bonding is notobtained even when jetting occurs. Under these conditions an extremelyhigh relative plate velocity, V is required in order to satisfy thecondition for jetting, i.e., to make a exceed t The excessive explosiveload needed to produce this high plate velocity often causes grossdeformation of the bonding assembly.

Furthermore, the strong detached shock waves which are reflected fromthe external free surfaces of the colliding plates as rarefaction wavescause disruption of any transient bond that is formed and contribute tothe severe deformation and fracturing of the plates.

From the preceeding discussion it is obvious that the values which mustbe determined before process conditions can be adjusted to insurejetting and, therefore, bonding, are the sonic velocities of metalplates 1 and 2, the velocities with which the plates move into thecollision region, and the relative plate velocity. In addition, if thevelocities with which the plates move into the collsion region exceedthe respective sonic velocities of the plates, the angle at which plates1 and 2 collide and the critical collision angle which must be exceededin order to insure jetting must be determined.

The value of the sonic velocity, C, of a metal or metallic system may beobtained by means of the relation where K is the adiabatic bulk modulusin dynes/cm. and p is the density in grams/cmfi. Values of K may beobtained from values of Youngs modulus, E, and Poissons ratio, 1 bymeans of the relation (2) K:E/(l2v) Values of p and K or E and v arereadily available in the literature (see, for example, AmericanInstitute of Physics Handbook, McGraw-Hill, New York, 1957).

Alternatively, the sonic velocity may be ascertained from publishedvalues of the velocity of the plastic shock wave as a function of theparticle velocity imparted to the metal by the shock wave in the mannerdescribed by R. G. McQueen and S. P. Marsh, Journal of Applied Physics31 (7), 1253 (1960).

If literature data are unavailable, values of C may be obtained bycarrying out shock wave measurements as described by R. G. McQueen andS. P. Marsh (10c. cit.) and in references cited by them. Alternatively Cmay be ascertained from the relation 3 czvc t' i/sicg where C is thevelocity of the elastic compressional waves and C is the velocity ofelastic shear waves in the metal. The required velocities of the elasticshear waves may be measured by well known methods. For illustrativepurposes, sonic velocity values for representative metals are given inthe following table.

Metal: Sonic velocity, meters/sec. Zinc 3000 Copper 4000 Magnesium 4500Niobium 4500 Austenitic stainless steel 4500 Nickel 4700 Titanium 4800Iron 4800 Molybdenum 5200 Aluminium 5500 The methods for determining VV02, V and '1 are most easily understood in the light of a discussion ofthe dynamics and geometry of a few modifications of the novel processfor explosively bonding metal layers.

Consider, for example, assemblies in which metal layers l and 2 arepositioned so that a juncture in the sense defined above is formedbetween the two plates and a layer of explosive is positioned on theexternal surface of one of both plates. When the explosive layer orlayers are initiated the pressures produced by the detonations rapidlyaccelerate the adjacent metal plate or plates to high velocities.Usually the maximum velocity for a given plate is reached in a distanceequal to the thickness of the plate and velocities high enough tosatisfy the conditions for bonding are attained in distances equal toonly fractions of the thickness of the plate. If each explosive layer isuniform in thickness and other physical properties and if each layer isinitiated simultaneously over its entire surface, e.g., using a planewave generator, the adjacent metal plate moves in a directionessentially perpendicular to its original p ane position and collideswith the other metal plate at an angle, it, which is equal to theoriginal angle, 6, between the plates.

In the first case in which a layer of explosive positioned on theexternal surface of, for example, metal plate 1, is initiatedsimultaneously over its entire surface, metal late 1 moves at avelocity, V which is equal to the relative plate velocity, V andcollides with metal plate 2. In this first case, V and V are determinedsolely by the initial angle, 6, between the metal plates and therelative plate veloctity, V and may be calculated by means of therelations V =V /tan 5 and vcg vp/sin 5 In the second case in whichlayers of explosive positioned on the external surfaces of metal plates1 and 2 are both initiated simultaneously over their entire surfaces,metal plate 1 moves at a velocity, V and metal plate 2 moves at avelocity, V The relative plate velocity, V is equal to the vector sum ofV and Vpg and maybe calculated by means of the relation The metal platescollide along a plane which makes angles of 6 and 5 with the originalplanes of metal plates 1 and 2, respectively. These angles, like theoriginal angle, 6, between the metal plates, are measured in any planeperpendicular to the line of intersection between the original planes ofthe metal plates and may be calculated by means of the relations In thissecond case V and V are determined solely by the initial angle, 5,between the metal plates, the plate velocities, V and V and the relativeplate velocity, V and may be calculated by means of the relations Ineither the first or the second case the angle, 6 or t, is, of course,known and the plate velocities, V and V may be determined experimentallyby any of several methods well known to the art. One such method fordetermining the velocity of an explosively propelled metal plateinvolves the use of electrical contact pins and is described by D.Bancroft et al., Journal of Applied Physics 27 (3), 291 (1956). Anoptical method is described by W. A. Allen, ibid. 24 (9'), 1180 (1953),and a method involving the use of flash X-radiographs is described by A.S. Balchan, ibid. 34 (2), 241 (1963). In the first case V and V can becalculated directly from the experimentally measured V (=V In the secondcase V must first be calculated from the experimentally measured V and Vby means of relation (6).

If V and/or V are smaller than the respective sonic velocities of metalplates 1 and 2 in order to insure bonding it is merely necessary todetermine the minimum relative plate velocity, V necessary to overcomethe elastic strength of at least one of the metal plates. Since therelative plate velocity increases with increasing loading of a givenexplosive and with decreasing thickness and density of the explosivelypropelled metal plate(s) this minimum relative plate velocity can bedetermined experimentally by adjusting the explosive loading and platethickness and density until some value of V at which jettingconsistently occurs without accompanying gross deformation of the metalplates is found.

If, however, V and veg exceed the respective sonic velocities of themetal plates, oblique shock waves are formed in the plates and I must bedetermined before process conditions can be controlled so that t exceedsh thus meeting the condition necessary to insure detachment of the shockWaves from the collision line and permit jetting.

When the oblique shock waves are attached to the collision line theysharply deflect the metal plates by the angles and 15 respectively, andthe angle between the plates in the collision region, 1 is equal to thesum of these deflections which sum is designated as t (i.e., \t: :q Thevalue of I for a given system is dependent upon V and V and upon thematerial properties of the metal plates and it is the maximum value of Ifor the given system which is equal to b and which 1, 1 must exceed topermit jetting.

The deflection angles p and (p may be calculated from the properties ofoblique shock waves in metal plates by means of the relations in which Uis the velocity of the shock wave measured normal to the shock front andU is the change in the velocity of the material caused by the shockwave.

The velocities, U and U are related to the pressures and densities aheadof and behind the shock fronts in the metal plates by the mechanicalshock equations P0 s=P( s- M) and ( P' P0:P0USUM in which p and P and pand P are the densities and pressures ahead of and behind the shockfronts in the metal plates. The density ahead of the shock front, issimply the known density of the metal plate at ambient pressure andtemperature and the pressure ahead of the shock front, P is simplyambient pressure. Since the ambient pressure is generally around 1atmosphere it is negligible compared to the pressure behind the shockfront, P, and the second relation (14) becomes =Pu s M A considerablebody of published data is available,

usually in the form of Hugoniot curves, which give the relationshipbetween P and V(:l/p) behind shock fronts in many metals. Thus bysubstituting a number of values of P and V(: l/ in the mechanical shockequations a number of values of U and U for each of the metal plates areobtained. Alternatively U and U may be measured experimentally asdescribed by Walsh, J. M., Rice, M. H., McQueen, R. G., and Yarger, F.L., Physical Review 108 (2), 196 (i957), and the corresponding values ofP and p, calculated using the mechanical shock equations.

The values of U and U and the values of V and V are substituted in theequations for tan 5 and tan respectively, and a number of values of andare obtained. The values of ga and a at each of a number of givenpressures are added together to give a number of values of 1 Finally,the values of d are plotted against the corresponding pressures and theresulting curve goes through a maximum. It is this maximum value of 4which is equal to D and which t must exceed in order to insuredetachment of the shock waves from the collision line and thus to insurejetting. Since a is equal to 5, d can be changed by changing the initialangle between the metal plates.

If an explosive layer is initiated at a single point or along a line,instead of with a plane wave generator, detonation progresses across theexplosive layer at the detonation velocity, D, of the explosive in adirection essentially parallel to the original plane position of theadjacent metal plate 1 or 2. Thus the pressure produced by thedetonation acts progressively on the adjacent metal plate 1 or 2 topropel it toward the other metal plate,

i.e., the pressure acts first on those portions of the adjacent platewhich are closest to the point or line of initiation. Under theseconditions adjacent metal plate 1 or 2 is deflected by an angle 7 or andtravels at a velocity Vp or Vp in a direction which forms an angle ofwith the perpendicular to the original plane position of the plate.

The angle, 6, as defined above is an angle between metal plates 1 and 2in any plane perpendicular to the line of intersection of the planes ofthe two plates. This angle simply defines the initial arrangement of theplates and is independent of the method of initiation and the consequentpattern of propagation of detonation of an explosive layer placed on theexternal surface of metal plate 1 or 2. There is however an angle, A,which for a given arrangement of the plates at an initial angle, 5, canvary in a manner dependent upon the direction in which detonationprogresses across an explosive layer. Properly speaking, there are twosuch angles: x, which is the angle between the initial line ofintersection of the planes of the metal plates and any line on metalplate 1 along which detonation is propagating and which is the anglebetween the initial line of intersection of the planes of the metalplates and any line on metal plate 2 along which detonation ispropagating. However, for practical reasons which are discussed ingreater detail hereinafter, when explosive layers are positioned on theexternal surfaces of both metal plate 1 and metal plate 2, both layershave substantially the same detonation velocity and are initiated insubstantially the same manner, i.e., the patterns of propagation ofexplosive layers placed on metal plates 1 and 2 are substantially thesame and A =7t =7u The direction of the initial line of intersectionbetween the planes of the metal plates is defined so that whendetonation is proceeding away from the line of intersection the angle A,is generated by rotating the line of intersection counterclockwise untilit coincides with the line of detonation and A is positive and between 0and 1r or 0 and 180. Conversely, when detonation is proceeding towardthe line of intersection, the angle is generated by rotating the line ofintersection clockwise until it coincides with the line of detonation; Ais negative and between G and 1r or 0 and -180. Obviously, whendetonation is proceeding parallel to the line of intersection there isno angle between the two lines, i.e., x=0 or 11. FIGURES 4A to 4Eillustrate the values of A at various locations on the surface of thebonding assembly when the explosive layer a is initiated at a point, eg,

by means of an initiator 6 having lead wires 7 to a source of electriccurrent or along a line, e.g., by means of a line wave generator 12. Ineach of these drawings the line AB approximates the line of intersectionof the planes of the metal plates, the solid lines marked with arrowsindicate the directions or the lines along which detonation propagateswhen the explosive layer is initiated as shown in the drawing, and thebroken lines are extrapolations of the lines along which detonationpropagates. The geometrical relationships among Vc1, V02, D, V 5, t, and71 when an explosive layer positioned on the external surface of metalplate 1 is initiated so that x=90 are illustrated in FIGURE 5. Thegeometrical relationships among C ,V D, V V V 6, 5 5 t, and v whenexplosive layers positioned on the external surfaces of metal plates 1and 2 are initiated simultaneously so that A:90 are illustrated in FIG-URE 6.

When the explosive layer(s) is initiated at a point or along a line itis necessary, just as it is necessary when a plane wave generator isused, to determine the values of V and V for a given system. However,when a single explosive layer positioned on the external surface of, forexample, metal plate 1 is initiated at a point or along a line, V and Vdepend on 6, A, and D and when explosive layers positioned on theexternal surfaces of both metal plates are initiated simultaneously at apoint or along a line on each layer, V depends on 6 A, and D and V02depends on 5 A, and D.

Considering the first case, i.e., a single explosive layer, the angle,5, is known and the angle, A, is readily determined since the pattern ofpropagation of detonation of an explosive layer initiated at any pointor line on the layer is obvious to one skilled in the art. The angle ofdeflection of metal plate l, can be measured by any of the experimentalmethods given above for measuring V131, or 7 can be calculated from theknown detonation velocity, D, and the experimentally determined platevelocity, V 1 by means of the relation 16 i V ZD sin or V =2D sing Thecollision velocities of plates 1 and 2 are obtained by substituting thevalues of 5, A, 7 and D, determined as indicated in the precedingparagraph, in the following equations and solving the equations for Vand V y sin antitari 7777 sin cos A eos A cos 5 [ll-cot n tan 5 sin \cosA] These equations are simplified when as is often convenient, theexplosive layer is initiated simultaneously along an entire edge of thelayer, e.g., by means of a line wave generator attached to one edge ofthe layer. When this edge is parallel to or coextensive with the line ofintersection of the planes of the metal plates detonation proceeds in adirection normal to the line of intersection over the entire surface ofthe layer, i.e., A=90 9 (see FIGURE 4A) and the equations for V and Vare reduced to the following forms.

(19) E 1a .$fl

D sin (I /1+6) cos 3 2 (20) Vcz sin D Sin (n+ When this edge isperpendicular to the line of intersection detonation proceeds in adirection parallel to the line of intersection over the entire surfaceof the layer, i.e., v= or 180 (see FIGURE 4B) and the equations arereduced to the following forms.

and

(24) cos 6 (1+COt'y tan 6 sin7t ---cos A) :cos 6 (1+cot tan 8 sin cosIt) Knowing 6 5 '7 A, and D, V and V can be calculated by means of therelations Sin i (l-tan%tan 6, sin -)sin sin cos A cos 7\ sin +cos 'y tan5 sin )t- (l-tan 71/2 tan 5 sin )t)sin cos and sin l (ltan gtan 6; sinA)sin v sin A cos A cos A sin 72+ cos tan 6 sin A- (1tan tan 6; sinA)sin 72 cos x Having determined V and V either the first or second caseif V and/or V are smaller than the respective sonic velocities of metalplates 1 and 2 bonding is achieved as long as V exceeds a minimum valuenecessary to overcome the elastic strength of at least one of the plate.In the first case V =V and the minimum value of V may be determined andV changed as described above with reference to plane wave initiation ofa single explosive layer positioned on the external surface of metalplate 1. In the second case V is a function of V and V which may becalculated by means of the relation V +V +2V V cos d-antitanfian 5 sinA) of metal plates 1 and 2, I must be determined as described above andb, adjusted so that it exceeds the calculated value of P While \l/ isequal to 6 when plane wave initiation of the explosive layer isemployed, when the explosive is initiated at a point or along a line thecollision angle t may be determined by means of the relation and may beincreased by increasing V by adjusting process conditions as describedabove.

The process of the invention is applicable to bonding a wide variety ofmetals, such as steel, copper, aluminum, iron, titanium, niobium,chromium, cobalt, nickel, beryllium, magnesium, molybdenum, tungsten,copper, gold. and their alloys, and other metals, many of which are verydifficult to bond by any of the conventional techniques. As statedpreviously, each of the metal layers may be a single metal, an alloy oftwo or more individual metals, or a composite of two or more singlelayers. The only limitation on the physical properties of the metallayers is that they be ductile, i.e., that they withstand permanentdeformation without fracturing under an explosive load. The surfaces ofthe metal layers do not require any preparation to remove surfaceimpurities prior to being subjected to the bonding procedure. However,if desired, the surfaces may be subjected to a degreasing and/or a mildabrasive treatment.

The metal layers can be of any desired dimensions and need not be flatplates of uniform thickness. For example, either or both of the layerscan be wedge-shaped, i.e., of graduated thickness, curved, dished, orbent at some angle. Moreover, more than 2 metal layers can be bondedtogether in a single operation, for example by providing an interleafbetween two outer layers to be bonded. One or more of the metal layersmay be a portion of the surface of a unit of equipment to which acoating layer is to be afiixed.

Many arrangements of the metal layers to be bonded may be used in thepractice of the present invention. The metal layers may actually meet toform a juncture along a line or at some point such as a corner on theinternal surface of each of the layers. Alternatively the metal layersmay be spaced a small distance from one another at the point or line oneach of the layers which is closest to the line of intersection of theplanes of the layers. However, since jetting does not occur unless thelayers achieve some minimum velocity, V relative to one another beforecolliding, when the former arrange ment is used a small region adjacentto the line or point of contact between the metal layers remainsunbonded in an otherwise continuously metallurgically bonded system.

The angle, 6, which defines the juncture between the metal layers to bebonded need not be constant over the entire area of each of the layers.For example, when the internal surface of one or both of the metallayers is curved or dished, 5 is the angle between the plane tangent tothe internal surface of the layer at a given point on the layer and theplane of the internal surface of the metal layer to which it is to bebonded, 5 being measured in any plane perpendicular to the line ofintersection of these two planes. When more than 2 metal layers are tobe bonded together in a single operation the angle, 6, between any twoadjacent layers may be the same as or different from the angle, 6,between any other two adjacent layers.

The method employed to maintain the angle, 6, between the metal layersprior to initiation of the explosive is not critical. The angle may beformed, for example, by resting one edge of a first metal layer againsta corresponding edge of a second metal layer so that the metal layersare in a standing" position on any supporting surface as shown in FIGURE2. Alternatively, a supporting means, e.g., spacer bars or struts asshown in FIG- URE 1, may be used to maintain 6 providing that thesupporting means do not interfere with the bonding procedure, i.e., byshielding large areas of the surface to be bonded or retarding theacceleration of the metal layerts) upon initiation of the explosivelayerts). In cases where the metal layers to be bonded compriseoverlapping ends of the same or of two different metal sheets, e.g., inseaming pipes or plates, 6 may be provided by bending one overlappingend away from the opposing overlapping end. Rigid supporting means forthe entire assembly to be bonded such as are shown as 3 in FIGURES l and2 are not necessary and the entire assembly may, for example, beimmersed in water.

The composition of the explosive layer(s) is not criti cal. For example,a layer of any cast, granular, gelatinous, fiexible or fibrous explosivecomposition based on pentaerythritol tetranitrate,cyclotrimethylenetrinitramine, trinitrotoluene, or ammonium nitrate, ormixtures thereof with each other with other explosive or nonexplosivecomponents may be used in the process of the present invention.

An explosive layer may be positioned on the external surface of one orboth metal layers and may be held in position by any suitable means suchas tape, glue, etc.

Obviously when more than two metal layers are bonded together in asingle operation to form a single bonded composite the explosive layeris placed only on the external surface of one or both of the outer metallayers.

Alternatively, an assembly of metal layers to be bonded may be placed oneach of the two opposite surfaces of a single explosive layer, thuspermitting two bonded composites to be formed simultaneously. In thislatter case when a single layer of explosive is used, the collision ofthe outer metal layer upon which the explosive is placed with aninterleaf metal layer is considered to be a collision between a movingmetal layer and a substantially stationary metal layer and the collisionof the composite comprising this first metal layer and the interleafwith other outer metal layer is considered to be a second collision ofsubstantially the same type. When two layers of explosive are used, thecollisions of both outer metal layers with the respective adjacentsurfaces of an interleaf metal layer are considered to be collisionsbetween a moving metal layer and a substantially stationary metal layer.

One limitation which must be made on the initial angle which defines thejuncture between the metal layers and on the loading, detonationvelocity, and method of initiation of the explosive layer(s) used isthat they be adjusted so that the two critical requirements for bondingbe met.

As is apparent from the preceding discussion of the mechanism by whichbonding occurs, one critical requirement for bonding is that the ratioof the collision velocity to the sonic velocity of at least one of themetal layers be less than 1.2, i.e.

The second critical requirement for bonding, which must be consideredonly if the ratios of the collision velocities of both metal layers tothe respective sonic velocities of the layers are greater than 1 is thatthe angle between the metal layers in the collision region exceed somecritical value, i.e.

when

ol yrs 1 and C2 1 then Since the sonic velocity of a given metal layermustbe considered to have a known fixed value it is the collisionvelocity which must be controlled by a suitable adjustment of processconditions in order to meet the first critical requirement for bonding.

When a layer of explosive on the external surface of one or both metallayers is initiated simultaneously over its entire surface the collisionvelocities of the metal layers are functions of the initial angle, 5,between the layers and the velocities V and/or V at which the metallayers are propelled toward one another (see relations (4) and t5), and(9) and (10)). Thus the initial angle between the metal layers and theexplosive loading must be adjusted so that the ratios V /C and/or Veg/C2are less than 1.2.

When a layer of explosive on the external surface of one or both metallayers is initiated at a point or along a line the collision velocitiesof the metal layers are functions of the initial range, 6, between themetal layers, the angle, 71 and/or by which the metal layer is deflectedby the detonation pressure, the angle, A, which depends upon the patternof propagation of detonation and the detonation velocity, D, of theexplosive. Thus in addition to the initial angle and the explosiveloading (to which 7 and 72 are directly proportional), the method orlocation of the point or line of initiation and the detonation velocityof the explosive must be adjusted so that the relays V /C and/or Veg/C2are less than 1.2.

In order to meet the second critical requirement for bonding the anglebetween the metal layers in the collision region must be controlled by asuitable adjustment of process conditions. When the entire explosivelayer-(s) is initiated simultaneously the angle, 0, at which the metallayers collide is equal to the initial angle, 5, between the layers and,obviously d is increased by a corresponding increase in 6. However, whenthe explosive layer is initiated at a point or along a line on the layert is a function of the collision velocities of the metal layers and ofthe relative plate velocity and the effect of adjustment of processconditions on t depends upon the effects of these adjustments on V V andV (see relation (28)).

Within the limitation that the initial angle between the metal layers,and the loading, detonation velocity, and method of initiation of theexplosive layer(s) satisfy the two critical requirements for bondingmany variations are possible.

It has been found that when the initial angle between the metal layersis between about 1 and 40 the process of the present invention can becarried out without extensive deformation of the bonded system. However,when the initial angle is 60 or more the bonded system often is severelydeformed by the forces produced by detonation of the explosive layer orlayers. This deformation can be attributed at least in part to the factthat when metal layers are arranged at large angles with respect to oneanother those portions of each layer which are furthest from thejuncture between the layers must travel relatively large distancesbefore colliding with corresponding portions of the other layer. Oversuch relatively large distances air between the layers may act as acushion preventing stable acceleration of the layer or layers to theappropriate velocity for stable collision resulting in jetting. Thelayer or layers may "flap or oscillate enroute to the collision regionand this phenomenon as well as lagging edges caused by the boundaryeffects at free surfaces, i.e., edges of the layer or layers, contributeto the gross deformation and/or poor bonding observed when the initialangle between the metal layers is 60 or more. For the same reasons,although the metal layers need not actually meet but may be separated bya small distance at the point or line closest to the line ofintersection of their lanes, this distance should be kept to a minimumand generally a separation of more than about 1 inch is neithernecessary nor desirable.

The expression explosive loading as used herein relates to the weightdistribution per unit area of the explosive layer or layers. However, abuffer layer of some material such as a polyester foam or film,Masonite, water, tape etc. can be interposed between an explosive layerand the adjacent metal layer in order to prevent surface contaminationor roughening of the metal layer. Since such a butter layer may tend toattenuate the pressure produced by detonation of a given explosive at agiven weight distribution, use of such a buffer layer may effectivelyreduce the explosive loading. Conversely, increasing confinement of anexplosive layer may effectively increase the explosive loading. Oneexplosive loading often is satisfactory for a number of differentbonding systems. As is shown in the examples, the amount of explosiveused for bonding two stainless steel plates of identical size isapproximately the same for the case when the initial angle between themetal layers is and when the angle is 32. The particular amount, orweight distribution, and loading of explosive suitable in any case willbe readily apparent to one skilled in the art, considering such factorsas type of explosive, thickness of the metal layer, etc. In any case, asexplained above, the explosive loading must be suflicient to produce acollision pressure which exceeds the elastic limit of at least one ofthe metal layers. Obviously, excessive explosive may cause undesireddeformation and should be avoided.

The explosive used must be a detonating explosive. Generally, theminimum detonation velocity of the explosive composition is at leastabout 1200 meters per second since below this velocity detonation isoften unstable and the effect of the composition on the metal workpieceis often unpredictable. Generally the maximum detonation velocity is nomore than about 9000 meters per second since the shock waves associatedwith explosive compositions having extremely high detonation velocitiesoften cause spalling of one or more of the metal layers. The practicalmaximum detonation velocity for a given system will be obvious to oneskilled in the art considering such factors as strength of the metallayers, etc. However if more than one explosive layer is used in asingle operation the two layers should have at least approximately thesame detonation velocity. Otherwise, the detonation front of the layerhaving the higher velocity may reach a point adjacent to an undetonatedportion of the other layer and dislodge the undetonated portion fromposition. This effect, as well as anomalous effects due to interferingshock waves, is detrimental to formation of a continuously bonded,substantially undeformed composite. Although in some cases, thedeleterious effects of explosive layers having different detonationvelocities can be overcome, e.g., by simultaneous plane wave intiationof both layers or some other specially designed method of initiation,such a situation introduces unnecessary complications and is generallyto be avoided.

The explosive layers may be initiated by any conventional initiatingdevice, e.g., blasting cap, exploding wires, detonating cord, line wavegenerator, plane wave generator or any suitable combination thereof. Thelocation of initiation on one or both layers may be at a point, tag, ata point along an edge, a comer, or in the center of the layer, along aline such as an edge of the layer, or simultaneously over the entiresurface of the layer. However, when more than one explosive layer isused, both layers generally should be initiated substantiallysimultaneously at substantially corresponding locations on the twolayers so that the pattern of propagation of detonation of the twolayers is essentially the same. Otherwise difiiculties comparable tothose mentioned above with reference to use of 2 layers of explosivehaving different detonation velocities may be encountered.

The process of the invention is particularly suitable for seam weldingof metal sheets to form large flat, continuous surfaces or rectangularcontainers and for seam welding of pipes or tubes. In such. operationswhere the length of the surfaces to be bonded is substantially greaterthan their width, the explosive layer(s) is conveniently initiated at apoint on the layer so that A20 over a substantial portion of the layer,i.e., detonation proceeds along the length of the layer parallel to thejuncture between the metal layers. This technique forces the air outfrom between the layers and insures a sound bond over the length of theseam.

The process of the invention is also particularly suitable for bondingthick metal layers, i.e., V2 inch thick or thicker. By employing arelatively large initial angle, 6 between the layers and adjustingprocess conditions so that the jet escapes completely from between thelayers a thin bond zone comprising essentially a direct metal-tometalbond rather than a thick layer of solidified melt which may containsolidification or other defects can be obtained. Also, when a metallayer of relatively high density is propelled against a stationary metallayer of relatively low density, by employing a relatively large initialangle, 6, and adjusting process conditions so that the jet oscillates, asound bond is obtained.

The strength of the substantially continuous metallurgical bond formedby the process of the present invention generally is greater than thatof the weaker of the metal layers in the composite. The ductility of thebonded composite generally is comparable to that of the unbonded metallayers and it may be improved by heat treatment. Thus, if desired thebonded metals may be subjected to further mteallurgical operations suchas forming, drawing, extruding, rolling, etc.

The invention may be illustrated by the following. In each of theexamples the character of the bond between the metal layers isdetermined by ultrasonic testing and by metallographic examination ofphotomicrographs of polished and etched portions of the cross-sectionsof the composites produced.

EXAMPLE 1 This bonding technique involves a single moving disk beingdriven against a stationary disk. The explosive employed is a thin,uniform sheet of a flexible explosive composition comprising 35%pentaerythritol tetranitrate, 50% red lead, and, as a binder, 15% of a50/50 mixture of butyl rubber and a thermoplastic terpene resin [mixtureof polymers of flpinene of formula (C H commercially available asPiccolyte S-lO (manufactured by the Pennsylvania Industrial ChemicalCorporation). This composition has a detonation velocity of about 5000meters per second. Complete details of this composition and a suitablemethod for its manufacture are disclosed in US. Patent 3,093,521.

A type 321 stainless steel disk 5% inches in diameter x 0.050 inch thickis placed on a supporting flat metal plate. A copper disk having thesame dimensions as the steel disk is positioned in such a manner as toform an angle of 730 between the inner surfaces of the plates, i.e., thesurfaces facing one another when the plates rest against each otheralong a section of the perimeter. The angle is maintained by taping thecontiguous edges of the disk and placing a spacer bar opposite thecontiguous surfaces. The surfaces of the disks are not treated in anymanner to remove surface impurities. A conforming layer, i.e., 5 /a-inchdisk of the above-described explosive composition, is attached to theouter surface of the copper dlsk by tape. The weight distribution of theexplosive layer is 2 grams per square inch. After initiation of theexplosive layer by a No. 6 electric blasting cap at the point where themetal layers are in contact, it is found that substantially continuousmetallurgical bonding over the entire area of the interface between thetwo disks is achieved.

The metal composite thus produced is successfully formed into a cuplikeconfiguration without any apparent fracture or separation of the bond bypositioning a layer of a detonating explosive on the metal composite andinitiating the explosive to drive the composite against a cup-shapedsteel mandrel.

ylhexyl)-2-acetoxy-l,2,3-propanetricarboxylate. This composition has adetonation velocity of about 6,900 meters TABLE I Metal Layer 1 MetalLayer 2 Angle Explosive between metal Treatment Treatment: layers, Sizeofeach Weight Example Type Size (1a.) of surface Type Size (in.)ol'surtace deg. layer (in.) distribution 304tstzlnless 2% x 2% x $62None .t 304tst21|inless 2% x 2% x Han. None 5 2% x 2%. 3

5 ea s ee 29 x 2% x V z. 2% x 2% x 1512 29/ 2: 2V. 3 2 x 2% x in. 2% x2% x162 16 29 x 2% 3 i X 4 x 5 52. 2% X 2% x $62 32 2% x 2, 1 8 0xl2x ,i6112x515." 9 0x12. 3 fixlx$i A t c 6X12XVL 9 0 6 3x3 3x3xyj 12 3x3t 63x3xy 3x3x 2 3x3 H 6 6x6x 6x6x% 9 12 6x6xy n fixfixl 15 12 1% (diam 1 x5 1% (tit-um.) x ,46 2T 3 5 t 1 5% (diam.) x 0.05.. 14 5% diain 3 s be2% x 231x 0.025 do 304tstainless 2% x 2% x }2 2% x 2?". 3

s ee Coppcr. 5% ((limn.) x 0.05 do 32ltstililnless 5% (diam) x 0.05. 145% diam. 2

s ee Titanium 5% (diam) x 0.05. Annealed. Aluminum". 5V (dianr) x 0.10..14 5% dlam 2 Mild steel. 1V (diam) x115" 1 /5 (diam.) x 146.. 40 l idiam3 Nickel .2 x5 /tn 4:15:41 40 4x5 5 do.- 4x5xlie 1010 [101 4x5..,. 5

The following example illustrates the seaming of a metal sheet to form apipe.

EXAMPLE 2 A 7-inch x la -inch aluminum sheet is Wrapped around a2-inch-diameter steel mandrel so that there is a l /z-inch overlappingportion of aluminum sheet. A 42-inch space remains at the edge of theoverlapping portion; the overlapping portion is in contact with the edgeof the layer adjacent the mandrel. Thus the angle varies slightly but,in general, lies between 10 and The steel mandrel has a light coat ofpetrolatum to prevent the aluminum from bonding to the steel mandrel. A7-inch x l /z-inch strip of explosive is placed along the edge of theentire length of the overlapping portion of the aluminum sheet. Theexplosive is a uniform sheet of an explosive composition comprising, byweight, 75% pentaerythritol tetranitrate, 7.5% paper pulp, and 17.5% ofa low-temperature polymerized acrylonitrile-butadiene elastomercontaining a high percentage (approximately 40%) of acrylonitrile andhaving a specific gravity of 1.00, and a Mooney viscosity of 7095(commercially available as Hycar" 1041 and manufactured by the B. F.Goodrich Co.). The weight distribution of the composition is 2 grams persquare inch. This explosive composition is described in US. Patent3,102,833. After initiation of the explosive layer by an electricblasting cap positioned in the center of one of the l /z-inch edges ofthe layer, a firmly seamed pipe results wherein the seam comprises asubstantially continuous metallurgical bond over the entire area of theinterface between the overlapped ends of the aluminum sheet.

To illustrate seam welding of metal sheets to form flat continuoussurfaces, the following examples are given.

EXAM PLE 3 An aluminum sheet, 6 inches x 2 4 inches x -inch, is placedon a steel support. A second 6 x 2 4 x -inch aluminum sheet having a1-inch, slightly bent portion (7 angle) along the entire length ispositioned in such a manner so that the fold of the bent portion isadjacent the entire length of the first sheet and the bent portionoverlaps 1 inch of the first sheet, forming an angle of approximately 7with the first sheet. A l-inch x 6-inch strip of explosive is fastenedto the outer surface of the bent portion, i.e., the bent portion ispropelled in a direction toward the first sheet upon initiation of theexplosive along the edge adjacent the fold. The explosive employed is aslightly modified version of that described in Example 1 and comprises alayer of a flexible explosive composition comprising 20% very finepentaerythritol tetranitrate, red lead, and, as a binder, a mixture of8% of the binder described in Example 1 and 2% of polyhutene having anaverage molecular weight of approximately 840, a specific gravity of0.90-0.87, and a viscosity index of 108 (commercially available asPolybutene 24 and manufactured by Oronite Chemical Company). Thedetonation velocity of the explosive composition is 4000 meters persecond and the weight distribution is 5 grams per square inch. Afterinitiation of the explosive layer by an electric blasting cap positionedin the center of the 6-inch edge of the explosive which is adjacent tothe bend in the second aluminum sheet, a firmly bonded one-inch seamcomprising a substantially continuous metallurgical bond over the entirearea of the interface between the overlapped ends of the two sheets,joins the two sheets.

EXAMPLE 4 The procedure of Example 3 is followed to seam two coppersheets, each 6 inches x 2 inches x inch, except that the 1 inch x 6 inchstrip of explosive used is a layer of a flexible composition comprising72% pentaerythritol tetranitrate, 6.5% nitrocellulose, and 21.5% oftri(2-ethper second. The explosive composition is the subject of US.Patent 2,992,087. The weight distribution of the explosive compositionis 1.5 grams per square inch. After initiation of the explosive layer byan electric blasting cap, the two sheets are found to be firmly bondedby a oneinch seam comprising a substantially continuous metallurgicalbond over the entire area of the interface between the overlapped endsof the two sheets.

Table I represents variations applicable in the angular bondingtechnique of the invention, e.g., angle range, types of metal, weightdistribution of explosives, etc.

The explosive used in all of the examples given in Table I, exceptExamples 10, 11, 21, and 22 is that described in Example 1. In Examples10 and 11, the explosive used is a slightly modified version of thatdescribed in Example 1 and comprises a flexible explosive compositioncomprising 20% very fine pentaerythritol tetranitrate, 70% red lead, and10% of the binder described in Example 1. In Examples 21 and 22, theexplosive used is that described in Example 3.

The bonding assemblies are similar to that shown in FIGURE 2 and in allof the examples, except Examples 5, 15, 20, 21 and 22, the explosivelayers are initiated by a combination of a No. 6 electric blasting capand detonating cords positioned as shown in FIGURE 2. In Example 5, theexplosive layers are initiated by two line wave generators (such asdescribed in US. Patent 2,943,- 571, issued July 5, 1960), one of whichis attached to that edge of each explosive layer adjacent to thejuncture between the metal layers, which in turn are initiatedsimultaneously by an electric blasting cap. In Examples and thecombination of electric blasting cap and detonating cords is used.However, in these examples a cord is attached to the center of eachexplosive layer rather than to an edge of the layer as shown in FIGURE2. In Examples 21 and 22 the explosive layers are initiated by means ofa strip of the explosive composition described in Example 4 which ispositioned so that it is in contact with that edge of each explosivelayer adjacent to the juncture between the metal layers over the entirelength of that edge. The strip is in turn initiated by means of a linewave generator and an electric blasting cap as described in connectionwith Example 5.

In all of the examples the metal layers are found to be substantiallycontinuously metallurgically bonded over the entire area of theinterface between the metal layers after initiation of the explosivelayers. When the shear strengths are determined according to A.S.T.M.Method No. A263- 44T, the shear strengths of the bonded assemblies arefound to be much higher than the minimum (20,000 p.s.i.) prescribed byA.S.T.M. specifications for this type of bonded assembly. For instance,the shear strengths of the bonded asemblies produced in Examples 11 and12 are 54,100 and 60,400 p.s.i., respectively. Bonded assembliesproduced by common conventional means usually exhibit a strength of onlyfrom 30,000 to 35,000 p.s.i.

Table II presents data relative to bonding more than 2 metal layers in asingle operation.

In all of the examples given in Table II the bonding assemblies arearranged substantially as shown in FIG- URE 2. However, a third metallayer or interleaf is interposed between metal layers 1 and 2. Theexplosive used in each of the examples is that described in Example 1and the explosive layers are initiated as shown in FIGURE 2 and asdescribed above in connection with Examples 6-14 and l619. Afterinitiation of the explosive layers each of the outer metal layers isfound to be substantially continuously metallurgically bonded to theinterleaf over the entire area of the interface between the layer andthe interleaf.

spacer bars spot welded to corresponding points on the adjacent edges ofthe two plates. The plates are positioned so that the minimum separationbetween them is 0.05 inch along the entire length of adjacent 6-inchedges of the plates, i.e., they substantially meet along a line and theangle between the plates is 10. The external surface of the stainlesssteel plate is covered with a layer of polystyrene foam l-inch thickwhich in turn is covered with a layer of the explosive compositiondescribed in Example 4 having a weight distribution of 5 grams persquare inch. The explosive is initiated by means of an electric blastingcap positioned in the center of the explosive layer and after detonationthe plates are substantially continuously metallurgically bonded overthe entire area of the interface between them.

EXAMPLE 31 A substantially continuously metallurgically bonded system isprepared using the materials and technique described in Example 30.However in this example the layer of explosive is initiated by means ofa plane wave generator as described in U.S. Patent 2,887,052 issued May19, 1959.

EXAMPLE 32 A substantially continuously metallurgically bonded system isprepared using the materials and a modification of the techniquedescribed in Example 30. In this example the plates are positioned sothat the minimum separation between them is 0.05 inch. However thisminimum separation is between one corner of the stainless steel plateand the corresponding adjacent corner of the mild steel plate, i.e.,they substantially meet at a single point, rather than along adjacentedges of the plates over the entire lengths of those edges as in Example30. The angle between the plates in any plane perpendicular to the lineof intersection of the planes of the two plates is 5 and the electricblasting cap is positioned at that corner of the explosive layer whichis adjacent to the juncture between the plates.

The invention has been described fully in the foregoing and it isintended to be limited only by the following claims.

What is claimed is:

1. A metthod for forming a substantially continuous metallurgical bondbetween metal layers which comprises forming a juncture between at leasttwo ductile metal layers, said juncture being defined by an angle ofabout 1 to positioning a layer of a detonating explosive on the externalsurface of at least one of the metal layers, and initiating theexplosive so that at least one of the TABLE II Metal Layer 1 InterleatMetal Layer 2 Angle Anglo Explosive between between metal metal layer 1layer 2 Size of Weight Ex Type Size (in) Type Size (111.) Type Size (in)and and each layer distritnterleiit inter-leaf (111.) butiOn (g-l 23.Titanium 2 x T x 0.025 304 stainless steels 2 x 7 x 562" 'Iitanium 2 x 7x .025 3 2 x 7 2 24 do 2x7x0.025 2x7x ,2 do 2x7x.025 5 2x7, 3 2x7x0.0252x7x$ti2 .r.. do .1 2x7x.(l25 7 7 x7 2 2 x2 x 0.025. 2%x2%x',-ti2. d02%x2 1x0.025-. 10 2%:(214 3 5% (diam.) 5% (diarn.) 321 stain- 5% (diann)73ll's 2 x 0.05. posite Cu/mild x 0.05. less steel. x 0.05. (diamsteel/Cu. 28. Copper 55 tdiam.) Mild steel 5% (diam Copper. 5% tdiam.)T30' 730' g 2 x 0.05. x 0.062. x 0405. (diam 29. 304 stainless 3:131: ,1Alloyz72 3143x0004 304 stainless 31:31:}15 5 5 3x3 3 steel silver/28steel. copper.

EXAMPLE 30 ratios of the collision velocities to the respective sonic Amild steel plate 6 inches wide, 9 inches long, and inch thick is placedon a plywood slab and a 304 stainless steel plate 6 inches wide, 9inches long and /s inch thick velocities of the metal layer is less than1.2 and when each of these ratios is greater than 1.0 the angle betweeneach two adjacent metal layers in the collision region exis supportedabove the mild steel plate by means of steel 75 ceeds the maximum valueof the sum of the deflections produced in the metal layers by obliqueshock waves, the loading of said explosive being at least that whichproduces a collision pressure greater than 100% of the elastic limit ofthe metal having the lowest elastic limit in the system.

2. A method for forming a substantially continuous metallurgical bondbetween metal layers which comprises forming a juncture between twolayers of different ductile metals, said juncture being defind by anangle of about 1 to 40, positioning a layer of a detonating explosive onthe external surface of at least one of the metal layers and initiatingthe explosive so that at least one of the ratios of the collisionvelocities to the respective sonic velocities of the metal layers isless than 1.2 and, when each of these ratios is greater than 1.0, theangle between said metal layers in the collision region exceeds themaximum value of the sum of the deflections produced in the metal layersby oblique shock waves, the loading of said explosive being at leastthat which produces a collision pressure greater than 100% of theelastic limit of the metal having the lowest elastic limit in thesystem.

3. A method as in claim 2 wherein a layer of a detonating explosive ispositioned on the external surface of one metal layer.

4. A method as in claim 2 wherein a layer of a detonating explosive ispositioned on the external surface of each of two metal layers, each ofthe layers of explosive having substantially the same detonationvelocity, and the layers of explosive being initiated substantiallysimultaneously and at substantially corresponding locations on each ofthe layers of explosive.

5. A method as in claim 2 wherein the explosive is initiated at a pointon an edge adjacent to the juncture between the metal layers.

6. A method as in claim 2 wherein the explosive is initiatedsimultaneously along an entire edge adjacent to the juncture between themetal layers.

7. A method as in claim 3 wherein the explosive is initiated at a pointsubstantially contiguous to the center of gravity of said layer of adetonating explosive.

8. A method as in claim 4 wherein said locations comprise pointssubstantially contiguous to the centers of gravity of said layers ofexplosive.

9. A method as in claim 3 wherein the explosive is initiatedsimultaneously over the entire surface of said layer of a detonatingexplosive.

10. A method as in claim 4 wherein each of said layers of explosive isinitiated simultaneously over its entire surface.

11. A method as in claim 2 wherein said metal layers are positioned sothat they substantially meet along an entire edge of each of the layersand the explosive is initiated along an edge of the bonding assemblyerpendicular to said first edge.

12. A method as in claim [2] 1 wherein said metal layers compriseoverlapping ends of a single metal layer.

13. A method as in claim 3 wherein at least one of said metal layerscomprises a plurality of single layers bonded together.

14. A method of claim 2 wherein said angle is about from 1 to 32 andsaid ductile metal layers are selected from the group consisting ofiron, titanium, niobium, tantalum, silver, nickel, magnesium, copper,zirconium and their alloys.

15. A process of claim 14 wherein said two layers are of titanium andsteel respectively.

16. A method of welding metal parts having surfaces to be joinedcomprising the steps of arranging said parts in such a manner as to forma V joint having an included angle greater than zero degrees, coatingthe outer surface of one of said parts with a: layer of explosive, anddetonating said explosive at the apex of said V joint whereby saidfacing surfaces are driven progressively into Contact at high relativevelocity and under a great pressure whereby bonding of the parts occurs.

17. A method of claim 16 wherein said V joint has an included angle ofabout from 1 to 32.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 6/1964 Cowan et al 29-487 X OTHER REFERENCES PAULM. COHEN, Primary Examiner US. Cl. X.R. 2942l, 486, 497.5

